With the advent of various kinds of on-line services targetting users who connect to the Internet, each and every service website uses a range of methods for user authentication. The most generalized authentication method is a method of requiring a user to input a user's identification (ID) and password when the user accesses a website to then perform a log-in operation, and checking whether the input ID and password are identical to user's existing established and registered ID and password, thereby performing user authentication.
However, when a user intends to join various websites and register as a member, by using his or her own identification (ID), he or she should change his or her own ID with a new ID and register as a member with the new ID if his or her own ID has been already registered by a different user.
Further, since each website frequently requires a string of different structures, for example, that an ID and a password be input with only alphabetical characters or only numbers, or only a mixture of alphabetical characters and numbers, at the time of subscribing for the website or performing a log-in operation, the user must inevitably register different IDs and passwords at each respective website.
As a result, it is not easy to decipher and input the appropriate registered ID and password at a website, among the many established and registered IDs and passwords. Also, since users forget infrequently used IDs and passwords at times, they must go through a very burdensome process of confirming their IDs and passwords to then perform a log-in operation.
Recently websites increasingly adopt users' e-mail addresses as their IDs, rather than a separate ID. However, since a separate password is still required, it is inconvenient for users when they lose and wish to alter their passwords.
An authentication method based on a public key infrastructure (PKI) which is a composite security system providing encryption and an electronic signature through a PKI algorithm does not require a user ID, and has merits in that it enables nearly perfect data security when encrypting and decrypting data since encryption and decryption differ from each other between the transmission and reception ends. However, since each user should manage his or her own password in the case of the PKI-based authentication method, he/she must receive authentication again at the time of having lost his or her password. In addition, it consumes much costs and time to construct a PKI-based authentication system, and it is difficult to manage issuance and cancellation authentications.